UH researchers introduce next generation of nanocomposite materials

Velcro-like material may revolutionize the nanocomposite technology

HONOLULU —Nanotechnologists in the College of Engineering at the University of Hawaiʻi at Mānoa have developed a multifunctional nanocomposite material using carbon nanotube forest-grown ceramic fiber cloths. The research article based on this finding is described in the May 7 online edition of the journal Nature Materials.

The researchers demonstrate one of the best ways to develop carbon nanotube-based composite materials. In doing so, they addressed various issues and concerns in both traditional composite materials and carbon nanotube reinforced nanocomposites.

According to the researchers, traditional composite materials, made by stacking up resin infiltrated fiber cloths, perform poor in "through-thickness" or the direction perpendicular to the fiber cloth, due to the absence of fibers in that direction. Their research work shows a novel remedy to this problem by grafting carbon nanotubes in the "through-thickness" direction. "Having carbon nanotube Velcro-like fasteners go in the through-thickness direction essentially would ensure the mechanical properties required in that direction," says Mehrdad Ghasemi-Nejhad, professor of mechanical engineering at the University of Hawaiʻi at Mānoa, and a lead author of the paper.

Though carbon nanotubes were projected as the best candidate for high performing structural composites, the efforts so far proved not so exciting. "Some fundamental issues such as dispersion, alignment and interfacial strength have kept researchers from realizing the full potential of nanotubes, particularly when combining them with other materials to make composites," says Pulickel Ajayan, the Henry Burlage Professor of Materials Science and Engineering at Rensselaer Polytechnic Institute, and also a lead author of the paper.

In their research, Nejhad and his team demonstrate a novel approach in grafting highly aligned forest of carbon nanotubes on silicon carbide ceramic fiber cloths. They follow a chemical vapor deposition process for the growth of carbon nanotube forest on the fiber cloths. The fiber cloths were then infiltrated with a high temperature polymer and then stacked on top of each other with the carbon nanotubes "sandwiched" in between the layers. The team has successfully made cloths up to roughly five inches by two inches and says that the process is easily scalable to make larger structures. The composites that were manufactured were cured in a furnace. "The most exciting part of a fabrication of this sort is that we start from a nano regime and develop a step-by-step macro structural composite from bottom up. This could be a perfect example of hierarchical manufacturing," Nejhad says.

The team has demonstrated a number of different functionalities of this new nanocomposite material. From a series of testing, they showed that their new 3-D nanocomposite material exhibit four times better performance in fracture tests and five-fold increase in their ability to dissipate energy by structural damping over the original ceramic composites without nanotubes forests. The new nanocomposite material has three times better dimensional stability compared to the base material without nanotubes. This could well be the most preferred composite structure for the future structural applications, the researchers say.

They also demonstrated that the novel 3-D nanocomposite performs much better in terms of thermal and electrical conductivities. This essentially gives an indication that the new nanocomposite has the capacity to participate in the structural system thermal managements as well as to perform self-structural health monitoring helping to identify cracks and defects in the structure.

This work was a collaborative research conducted by the University of Hawaiʻi (UH) at Mānoa in Honolulu, Hawaiʻi, and the Rensselaer Polytechnic Institute (RPI) in Troy, New York. The UH research team was led by Dr. Nejhad, who also directs the Hawaiʻi Nanotechnology Laboratory (HNL) and the Intelligent and Composite Materials Laboratory (ICML). The UH team includes: Vinod Veedu, a doctoral student at the HNL; Anyuan Cao, assistant professor of mechanical engineering and associate director of the HNL; and Kougen Ma, an assistant researcher and associate director of the ICML. The RPI team was lead by Dr. Ajayan. The RPI team includes: Caterina Soldano, a doctoral student in physics, applied physics, and astronomy; Xuesong Li, a doctoral student in materials science and engineering; and Swastik Kar, a postdoctoral researcher in materials science and engineering.

Nejhad received funding for the project from the Office of Naval Research through the Adaptive Damping and Positioning using Intelligent Composite Active Structures (ADPICAS) project.